1. Field of the Invention
The present invention relates to a water jet propulsion watercraft, and more particularly, to a water jet propulsion watercraft arranged such that a hull is propelled by water being jetted rearward by a jet propulsion device driven by a driving force of an engine.
2. Description of the Related Art
A water jet propulsion watercraft is a marine vessel in which a propulsive force is generated by a jet propulsion device. The jet propulsion device is driven, for example, by a driving force of an engine. The jet propulsion device takes in water around a hull and jets the water to the rear of the hull to apply a propulsive force to the hull.
Ordinarily, with the water jet propulsion device, exhaust gas is exhausted into water to suppress engine exhaust noise. Therefore, an exhaust pipe thus has an opening in the water. There is thus a possibility of water entering into the engine via the exhaust pipe. Thus, in a water jet propulsion watercraft, a box-shaped water lock is provided at an intermediate portion of the exhaust pipe. The water lock can retain water that enters from the opening of the exhaust pipe. Entry of water to the engine side of the water lock is thereby suppressed.
With such a water jet propulsion watercraft, when the water jet watercraft is landed after use (after marine vessel running), the water retained in the water lock remains, and this water may have an adverse effect on the engine, etc. A user of the water jet propulsion watercraft thus performs engine revving, that is, so-called racing on land after landed the watercraft after use. The water remaining inside the water lock can thereby be discharged by an exhaust pressure of the engine.
However, unlike when the hull is in water, the jet propulsion device does not receive resistance of the water during racing on land. Thus, in comparison to use on water, an engine rotational speed increases readily. When the engine rotational speed increases excessively, a load is placed on the engine and an excessively loud noise is generated as exhaust noise.
For resolving this problem, there is known a water jet propulsion watercraft that includes a controller that restricts the engine rotational speed to not more than a predetermined rotational speed when it is determined that the hull is not in water (see, for example, U.S. Patent Application Publication No. 2002/0045390 A1).
With the prior art described in U.S. Patent Application Publication No. 2002/0045390 A1, a pressure sensor or a watercraft speed sensor, attached to an outer side of the hull, is used to determine whether or not the hull is in water. More specifically, in a case where the pressure sensor is used, it is determined that the hull is on land when a state where a detection value of the pressure sensor is not more than an atmospheric pressure continues for not less than a predetermined time. In a case where the watercraft speed sensor is used, it is determined that the hull is on land when a state where a detection value of the watercraft speed sensor is not more than a predetermined value continues for not less than a predetermined time.